U.S. patent application number 09/779151 was filed with the patent office on 2002-10-17 for transparent, sealable, uv-resistant polyester film, its use and process for its production.
Invention is credited to Crass, Guenther, Kern, Ulrich, Murschall, Ursula, Peiffer, Herbert, Stopp, Andreas.
Application Number | 20020150751 09/779151 |
Document ID | / |
Family ID | 7631628 |
Filed Date | 2002-10-17 |
United States Patent
Application |
20020150751 |
Kind Code |
A1 |
Murschall, Ursula ; et
al. |
October 17, 2002 |
Transparent, sealable, uv-resistant polyester film, its use and
process for its production
Abstract
Biaxially oriented, coextruded polyester films with a base layer
at least 90% by weight of which is composed of a thermoplastic
polyester, preferably polyethylene terephthalate (PET), and with at
least one sealable outer layer and a second nonsealable outer layer
and, if desired, with other intermediate layers, and comprising at
least one UV absorber, preferably hydroxybenzotriazoles and
triazines, have high UV resistance, do not embrittle when exposed
to high temperatures, have a surface without undesirable haze and
are suitable for numerous indoor and outdoor applications. The
outer layers comprise antiblocking agents, such as silica with an
average particle diameter preferably below 50 nm and/or above 2
.mu.m, and the sealable outer layer is preferably composed of a
copolyester which has been built up from ethylene terephthalate
units and ethylene isophthalate units.
Inventors: |
Murschall, Ursula;
(Nierstein, DE) ; Kern, Ulrich; (Ingelheim,
DE) ; Crass, Guenther; (Taunusstein, DE) ;
Stopp, Andreas; (Ingelheim, DE) ; Peiffer,
Herbert; (Mainz, DE) |
Correspondence
Address: |
ProPat, LLC
2912 Crobsy Road
Charlotte
NC
28211
US
|
Family ID: |
7631628 |
Appl. No.: |
09/779151 |
Filed: |
February 8, 2001 |
Current U.S.
Class: |
428/331 ;
264/173.14; 264/173.15; 428/215; 428/480 |
Current CPC
Class: |
Y10T 428/25 20150115;
Y10T 428/24942 20150115; Y10T 428/24975 20150115; G09F 7/00
20130101; Y10T 428/2817 20150115; Y10T 428/24967 20150115; Y10T
428/2826 20150115; Y10T 428/24355 20150115; Y10T 428/31797
20150401; G09F 15/02 20130101; Y10S 428/91 20130101; Y10T 428/2495
20150115; Y10T 428/259 20150115; Y10T 428/31786 20150401 |
Class at
Publication: |
428/331 ;
428/480; 264/173.14; 264/173.15; 428/215 |
International
Class: |
B32B 007/02; B32B
027/36; B29C 055/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 19, 2000 |
DE |
100 07 724.2 |
Claims
What is claimed is:
1. A polyester film which has a base layer B made from a
thermoplastic polyester and which are one side of the base layer,
has a sealable outer layer A and, located on the other side of the
base layer, has a nonsealable outer layer C, where the outer layers
A and C comprise at least one antiblocking agent, and the film
comprises at least one UV absorber.
2. The polyester film as claimed in claim 1, further comprising one
or more intermediate layers arranged between the base layer B and
the outer layer A or between the base layer B and the outer layer C
or between the base layer B and the outer layer A and between base
layer B and outer layer C.
3. The polyester film as claimed in claim 1, wherein at least 90%
by weight of the base layer comprises polyethylene terephthalate or
polyethylene-2,6-naphthalate.
4. The polyester film as claimed in claim 1, wherein the outer
layer A comprises a copolyester which is predominantly composed of
isophthalic acid units, terephthalic acid units and ethylene glycol
units.
5. The polyester film as claimed in claim 4, wherein from 40 to 95
mol %, of the copolyester of outer layer A is composed of ethylene
terephthalate units, and the remainder making up 100 mol % is
composed of ethylene isophthalate units.
6. The polyester as claimed in claim 1, wherein the base layer B
comprises no antiblocking agents, or the concentration of
antiblocking agent in the base layer B is lower than in the outer
layers A and C.
7. The polyester as claimed in claim 1, wherein the concentration
of antiblocking agent in the nonsealable outer layer C is higher
than in the sealable outer layer A.
8. The polyester as claimed in claim 6, wherein the concentration
of antiblocking agent in the base layer B is from 0-0.15% by
weight, in the outer layer C from 0.1-1% by weight and from
0.01-0.2% by weight in the outer layer A.
9. The polyester film as claimed in claim 1, wherein the average
particle diameter of the antiblocking agents is below 100 nm and/or
above 1 .mu.m.
10. The polyester film as claimed in claim 1, wherein SiO.sub.2 is
used as antiblocking agent.
11. The polyester film as claimed in claim 1, wherein the thickness
of the outer layers is identical or different and is from 0.2 to
4.0 .mu.m.
12. The polyester film as claimed in claim 1, wherein the UV
absorber is present in the base layer and/or in the outer
layers.
13. The polyester film as claimed in claim 1, wherein the UV
absorber comprises 2-hydroxybenzotriazoles or triazines or mixtures
of these UV absorbers.
14. The polyester film as claimed in claim 13, wherein the UV
absorber comprises
2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol or
2,2-methylenebis(6-(2H-benzo-triazol-2-yl)-4-(1,1,2,2-tetramethylpropyl)p-
henol) or a mixture of these UV absorbers.
15. The polyester film as claimed in claim 1, wherein the
concentration of the UV absorber(s) is from 0.01-5% by weight,
based on the weight of the layers in which they are present.
16. A process for producing a polyester film as claimed in claim 1,
which comprises coextruding, through a coextrusion die, the
starting materials required for producing the base and outer
layers, and biaxially orienting and heat-setting, the resultant
film.
17. The process as claimed in claim 16, wherein the UV absorber is
added by way of masterbatch technology.
Description
[0001] The invention relates to a transparent, UV-resistant,
sealable, biaxially oriented polyester film composed of at least
one base layer B and, applied to both sides of this base layer,
outer layers A and C. The film also comprises at least one UV
stabilizer as light stabilizer. The invention further relates to
the use of the film and to a process for its production.
BACKGROUND OF THE INVENTION
[0002] The novel films are particularly suitable for outdoor
applications, e.g. for greenhouses or roofing systems. The films
also have very good suitability for the covering of, and therefore
for the protection of, metallic surfaces, onto which the films can
be hot-sealed. In outdoor applications, films which comprise no
UV-absorbing materials yellow, even after a short period, and their
mechanical properties become impaired as a result of photooxidative
degradation by sunlight.
[0003] Sealable, biaxially oriented polyester films are known in
the prior art. Likewise known are sealable, biaxially oriented
polyester films which have one or more UV absorbers. These films
known from the prior art either have good sealing performance, good
optical properties or acceptable processing performance.
[0004] GB-A 1 465 973 describes a coextruded polyester film having
two layers, one layer of which consists of copolyesters containing
isophthalic acid and terephthalic acid, and the other layer of
which consists of polyethylene terephthalate. The patent gives no
useful indication of the sealing performance of the film. The lack
of pigmentation means that the film cannot be produced by a
reliable process (cannot be wound up) and that the possibilities
for further processing of the film are limited.
[0005] EP-A 0 035 835 describes a coextruded, sealable polyester
film where, in the sealable layer, particles whose average size
exceeds the sealable layer thickness are present in order to
improve winding and processing performance. The particulate
additives form surface protrusions which prevent undesired blocking
and sticking of the film to rolls or guides. No further details are
given concerning the incorporation of antiblocking agents in
relation to the other, nonsealable layer of the film. It is
uncertain whether this layer comprises antiblocking agents. The
choice of particles having diameters greater than the sealable
layer thickness, at the concentrations given in the Examples,
impairs the sealing performance of the film. The patent does not
give any indication of the sealing temperature range of the film.
The seal seam strength is measured at 140.degree. C. and is in the
range from 63 to 120 N/m (from 0.97 N/15 mm to 1.8 N/15 mm of film
width).
[0006] EP-A 0 432 886 describes a coextruded multilayer polyester
film which has a first surface on which has been arranged a
sealable layer, and has a second surface on which has been arranged
an acrylate layer. The sealable outer layer here may also be
composed of isophthalic-acid-containing and
terephthalic-acid-containing copolyesters. The coating on the
reverse side gives the film improved processing performance. The
patent gives no indication of the sealing temperature range of the
film. The seal seam strength is measured at 140.degree. C. For a
sealable layer thickness of 11 .mu.m the seal seam strength given
is 761.5 N/m (11.4 N/15 mm). A disadvantage of the reverse-side
acrylate coating is that this side is now not sealable with respect
to the sealable outer layer, and the film therefore has only very
restricted use.
[0007] EP-A 0 515 096 describes a coextruded, multilayer film,
sealable polyester film which comprises a further additive in the
sealable layer. The additive may comprise inorganic particles, for
example, and is preferably distributed in an aqueous layer onto the
film during its production. Using this method, the film is claimed
to retain its good sealing properties and to be easy to process.
The reverse side comprises only very few particles, most of which
pass into this layer via the recycled material. This patent again
gives no indication of the sealing temperature range of the film.
The seal seam strength is measured at 140.degree. C. and is above
200 N/m (3 N/15 mm). For a sealable layer of 3 .mu.m thickness the
seal seam strength given is 275 N/m (4.125 N/15 mm).
[0008] WO 98/06575 describes a coextruded, multilayer polyester
film which comprises a sealable outer layer and a nonsealable base
layer. The base layer here may have been built up from one or more
layers, and the inner layer of these layers is in contact with the
sealable layer. The other (outward-facing) layer then forms the
second nonsealable outer layer. Here, too, the sealable outer layer
may be composed of isophthalic-acid-containing and
terephthalic-acid-containing copolyesters, but these comprise no
antiblocking particles. The film also comprises at least one UV
absorber, which is added to the base layer in a weight ratio of
from 0.1 to 10%. Preferred UV absorbers used here are triazines,
e.g. Tinuvin 1577 from Ciba. The base layer has conventional
antiblocking agents. The film has good sealability, but does not
have the desired processing performance and also has unsatisfactory
optical properties, such as gloss and haze.
DESCRIPTION OF THE INVENTION
[0009] It was an object of the present invention to provide a
transparent, UV-resistant, sealable and biaxially oriented
polyester film which does not have the disadvantages of the films
mentioned from the prior art and which, in particular, has a
combination of advantageous properties, such as very good
sealability, cost-effective production, improved processability and
improved optical properties.
[0010] It was a particular object of the present invention to
extend the sealing temperature range of the film to low
temperatures, to increase the seal seam strength of the film and at
the same time to provide for better handling of the film than is
known from the prior art. The film should also give good
processing, even on high-speed processing machinery. It should also
be certain that during extrusion of the film it is possible to
reintroduce recyclable material directly associated with its
production at a concentration of up to 60% by weight, based on the
total weight of the film, without any significant resulting adverse
effect on the physical properties of the film.
[0011] Since the film is intended particularly for outdoor
application and/or critical indoor applications, it should have
high UV resistance. High UV resistance means that sunlight or other
UV radiation causes no, or only extremely little, damage to the
films. In particular, when used outdoors for a number of years, the
films should show no yellowing, embrittlement or surface-cracking,
and have unimpaired mechanical properties. High UV resistance means
that the film absorbs the UV light and does not begin to transmit
light until the visible region has been reached.
[0012] The good mechanical properties include a high modulus of
elasticity (EMD>3200 N/mm2; ETD>3500 N/mm2), and also good
tear strengths (in MD>100 N/mm2; in TD>130 N/mm2).
[0013] According to the invention, the object is achieved by
providing a UV-resistant, biaxially oriented, sealable polyester
film with at least one base layer B, with a sealable outer layer A,
and with another outer layer C located on the other side of the
base layer B, where the sealable outer layer A preferably has a
minimum sealing temperature below 110.degree. C. and a seal seam
strength of at least 1.3 N/15 mm, and the film comprises at least
one UV absorber or a mixture of various UV absorbers.
[0014] It is appropriate for the UV stabilizer to be fed directly
as a masterbatch during film production, and the concentration of
the UV stabilizer here is preferably from 0.01 to 5% by weight,
based on the weight of the layers in which the UV absorber is
present. The film preferably has three layers, and the layers then
present are the base layer B, the sealable outer layer A and the
nonsealable outer layer C. The novel film may have additional
intermediate layers.
[0015] The base layer B of the film is composed of a thermoplastic,
and at least 90% by weight of the base layer is preferably composed
of a thermoplastic polyester. Polyesters suitable for this purpose
are those made from ethylene glycol and terephthalic acid
(polyethylene terephthalate, PET), from ethylene glycol and
naphthalene-2,6-dicarboxyli- c acid (polyethylene 2,6-naphthalate,
PEN), from 1,4-bishydroxymethylcyclo- hexane and terephthalic acid
(poly-1,4-cyclohexanedimethylene terephthalate, PCDT), or else made
from ethylene glycol, naphthalene-2,6-dicarboxylic acid and
biphenyl4,4'-dicarboxylic acid (polyethylene 2,6-naphthalate
bibenzoate, PENBB). Particular preference is given to polyesters at
least 90 mol %, in particular at least 95 mol %, of which is
composed of ethylene glycol units and terephthalic acid units, or
of ethylene glycol units and naphthalene-2,6-dicarboxylic acid
units. The remaining monomer units derive from other aliphatic,
cycloaliphatic or aromatic diols and, respectively, dicarboxylic
acids, as may also occur in the layers A and/or C. Other examples
of suitable aliphatic diols are diethylene glycol, triethylene
glycol, aliphatic glycols of the formula HO--(CH2)n--OH, where n is
an integer from 3 to 6 (in particular 1,3-propanediol,
1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol) and branched
aliphatic glycols having up to 6 carbon atoms. Among the
cycloaliphatic diols, mention should be made of cyclohexanediols
(in particular 1,4-cyclohexanediol). Examples of other suitable
aromatic diols have the formula HO--C6H4--X--C6H4--OH, where X is
--CH2--, --C(CH3)2--, --C(CF3)2--, --O--, --S-- or --SO2--.
Bisphenols of the formula HO--C6H4--C6H4--OH are also very
suitable.
[0016] Other aromatic dicarboxylic acids are preferably
benzenedicarboxylic acids, naphthalene dicarboxylic acids (such as
naphthalene-1,4- or -1,6-dicarboxylic acid),
biphenyl-x,x'-dicarboxylic acids (in particular
biphenyl-4,4'-dicarboxylic acid),
diphenylacetylene-x,x'-dicarboxylic acids (in particular
diphenylacetylene-4,4'-dicarboxylic acid) or
stilbene-x,x'-dicarboxylic acids. Among the cycloaliphatic
dicarboxylic acids mention should be made of
cyclohexanedicarboxylic acids (in particular
cyclohexane-1,4-dicarboxy- lic acid). Among the aliphatic
dicarboxylic acids, the C3-C19 alkanediacids are particularly
suitable, and the alkane moiety here may be straight-chain or
branched.
[0017] One way of preparing these polyesters according to the
invention is the transesterification process. Here, the starting
materials are dicarboxylic esters and diols, which are reacted
using the customary transesterification catalysts, such as the
salts of zinc, of calcium, of lithium, of magnesium or of
manganese. The intermediates are then polycondensed in the presence
of well known polycondensation catalysts, such as antimony trioxide
or titanium salts. Another equally good preparation method is the
direct esterification process in the presence of polycondensation
catalysts. This starts directly from the dicarboxylic acids and the
diols (W. Eberhard, S. Janocha, M. J. Hopper, K. J. Mackenzie,
"Polyester Films", in Encyclopaedia of Polymer Science &
Engineering Volume 12, 2, 193-216 (1988), John Wiley &
Sons).
[0018] The sealable outer layer A applied by coextrusion to the
base layer B has been built up on the basis of polyester copolymers
and essentially consists of copolyesters composed predominantly of
isophthalic acid units and of terephthalic acid units, and of
ethylene glycol units. The remaining monomer units derive from
other aliphatic, cycloaliphatic or aromatic diols and,
respectively, dicarboxylic acids, as may also occur in the base
layer. Preferred copolyesters are those which have been built up
from ethylene terephthalate units and from ethylene isophthalate
units. The proportion of ethylene terephthalate is preferably from
40 to 95 mol %, and the corresponding proportion of ethylene
isophthalate is preferably from 60 to 5 mol %. Particular reference
is given to copolyesters in which the proportion of ethylene
terephthalate is from 50 to 90 mol % and the corresponding
proportion of ethylene isophthalate is from 50 to 10 mol %, and
very particular preference is given to copolyesters in which the
proportion of ethylene terephthalate is from 60 to 85 mol % and the
corresponding proportion of ethylene isophthalate is from 40 to 15
mol %.
[0019] For the other, nonsealable outer layer C, or for any
intermediate layers present, use may in principle be made of the
polymers described above for the base layer B.
[0020] The desired sealing and processing properties of the novel
film are obtained from the combination of properties of the
copolyester used for the sealable outer layer and from the
topographies of the sealable outer layer A and the nonsealable
outer layer C.
[0021] The minimum sealing temperature of preferably below
110.degree. C. and the seal seam strength of preferably at least
1.3 N/15 mm are achieved when the copolymers described in more
detail above are used for the sealable outer layer A. The films
have their best sealing properties when no other additives, in
particular no inorganic or organic fillers, are added to the
copolymer. In this case, with the copolyester given above, the
lowest minimum sealing temperature and the highest seal seam
strengths are obtained. However, the handling of the film is poorer
in this case, since the surface of the sealable outer layer A tends
to block. The film can hardly be wound and has little suitability
for further processing on high-speed packaging machinery. To
improve handling of the film, and processability, it is necessary
to modify the sealable outer layer A. This is best done with the
aid of suitable antiblocking agents of a selected size, which are
added to the sealable layer at a particular concentration, and
specifically in such a way as to firstly minimize blocking and
secondly give only insignificant impairment of sealing properties.
This desired combination of properties can be achieved in
particular when the topography of the sealable outer layer A is
characterized by the following set of parameters:
[0022] The roughness of the sealable outer layer, characterized by
the Ra value, should be less than 30 nm, otherwise the sealing
properties are adversely affected for the purposes of the present
invention.
[0023] The value measured for gas flow should be from 500-4000 s.
At values below 500 s the sealing properties are adversely affected
for the purposes of the present invention, and at values above 4000
s the handling of the film becomes poor.
[0024] For further improvement in the processing performance of the
sealable film, the topography of the nonsealable outer layer C
should be characterized by the following set of parameters:
[0025] The coefficient of friction (COF) of this side with respect
to itself should be below 0.5, otherwise the winding performance
and further processing of the film are unsatisfactory.
[0026] The roughness of the nonsealable outer layer, characterized
by the Ra value, should be above 40 nm and below 100 nm. Values
below 40 nm have an adverse effect on the winding and processing
performance of the film, and values above 100 nm impair the optical
properties (gloss, haze) of the film.
[0027] The value measured for gas flow should be below 120 s. At
values above 120 s the winding and processing performance of the
film is adversely affected.
[0028] The number of elevations N per mm2 of film surface has the
following correlation with their respective heights h:
0.29-3.30.multidot.log h/.mu.m<log
N/mm2<1.84-2.70.multidot.log h/.mu.m
0.01 .mu.m<h<10 .mu.m
[0029] If the values for N are below those corresponding to the
left-hand side of the equation, the winding and processing
performance of the film is adversely affected, and if the values
for N are above those corresponding to the right-hand side of the
equation, the gloss and haze of the film are adversely
affected.
[0030] The UV stabilizers selected for rendering the novel film
UV-resistant may in principle be any organic or inorganic UV
stabilizer suitable for incorporation within polyesters. Suitable
UV stabilizers of this type are known from the prior art and are
described in more detail in WO 98/06575, in EP-A-0 006 686, in
EP-A-0 031 202, EP-A-0 031 203 or in EP-A-0 076 582, for
example.
[0031] Light, in particular the ultraviolet content of solar
radiation, i.e. the wavelength region from 280 to 400 nm, causes
degradation in thermoplastics, the results of which are not only a
change in appearance due to color change or yellowing, but also an
adverse effect on mechanical and physical properties.
[0032] The inhibition of this photooxidative degradation is of
considerable industrial and economic importance, since without it
many thermoplastics have drastically reduced scope of
application.
[0033] The absorption of UV light by polyethylene terephthalates
for example, starts at below 360 nm, increases markedly below 320
nm and is very pronounced at below 300 nm. Maximum absorption
occurs at between 280 and 300 nm.
[0034] In the presence of oxygen it is mainly chain cleavage which
occurs, but without crosslinking. The predominant photooxidation
products in quantity terms are carbon monoxide, carbon dioxide and
carboxylic acids. Besides the direct photolysis of the ester
groups, consideration has to be given to oxidation reactions which
proceed via peroxide radicals, again to form carbon dioxide.
[0035] In the photooxidation of polyethylene terephthalates there
can also be cleavage of hydrogen at the position a to the ester
groups, giving hydroperoxides and decomposition products of these,
and this may be accompanied by chain cleavage (H. Day, D. M. Wiles:
J. Appl. Polym. Sci 16,1972, p. 203).
[0036] UV stabilizers, i.e. light stabilizers which are UV
absorbers, are chemical compounds which can intervene in the
physical and chemical processes of light-induced degradation.
Carbon black and other pigments can give some protection from
light. However, these substances are unsuitable for transparent
films, since they cause discoloration or color change. The only
compounds suitable for transparent, matt films are those organic or
organometallic compounds which produce no, or only extremely
slight, color or color change in the thermoplastic to be
stabilized, i.e. are soluble in the thermoplastic.
[0037] For the purposes of the present invention, light stabilizers
which are suitable UV stabilizers are those which absorb at least
70%, preferably 80%, particularly preferably 90%, of the UV light
in the wavelength region from 180 to 380 nm, preferably from 280 to
350 nm. These are particularly suitable if they are thermally
stable in the temperature range from 260 to 300.degree. C., i.e. do
not decompose and do not cause evolution of gas. Examples of light
stabilizers which are suitable UV stabilizers are
2-hydroxybenzophenones, 2-hydroxybenzotriazoles, organonickel
compounds, salicylic 1
[0038] esters, cinnamic ester derivatives, resorcinol
monobenzoates, oxanilides, hydroxybenzoates, sterically hindered
amines and triazines, preferably the 2-hydroxybenzotriazoles and
the triazines.
[0039] In one very particularly preferred embodiment, the novel
film comprises from 0.01 to 5.0% by weight of
2-(4,6-diphenyl-1,3,5-triazin-2-- yl)-5-hexyloxyphenol of the
formula 2
[0040] or from 0.01 to 5.0% by weight of
2,2-methylenebis(6-(2H-benzotriaz-
ol-2-yl)-4-(1,1,2,2-tetramethylpropyl)phenol) of the formula
[0041] In one preferred embodiment, it is also possible to use a
mixture of these two UV stabilizers or a mixture of at least one of
these two UV stabilizers with other UV stabilizers, and here the
total concentration of light stabilizer is preferably from 0.01 to
5.0% by weight, based on the weight of polyethylene
terephthalate.
[0042] In the three-layer embodiment, the UV stabilizer is
preferably present in the nonsealable outer layer C. However, if
required, the base layer B and/or the sealable outer layer A
and/or, if desired, any intermediate layers present may also have
UV stabilizers. The concentration of the stabilizer(s) here is
based on the weight of the layers which have UV stabilizers.
[0043] Surprisingly, weathering tests to the test specification ISO
4892 using the Atlas Ci65 Weather-Ometer have shown that, to
improve UV resistance, in the case of the abovementioned
three-layer film it is fully sufficient for the outer layers of
preferred thickness from 0.3 to 2.5 .mu.m to have UV
stabilizers.
[0044] Weathering tests have moreover shown that when films have
been rendered UV-resistant according to the the invention they
generally show no yellowing, no embrittlement, no loss of surface
gloss, no surface-cracking and no impairment of mechanical
properties even after an extrapolated 5 to 7 years of outdoor
application in weathering tests.
[0045] It may be useful for the light stabilizer to be fed
straightaway during preparation of the thermoplastic, or it may be
fed into the extruder during film production.
[0046] It is particularly preferable for the light stabilizer to be
added by way of masterbatch technology. The light stabilizer is
dispersed in a solid carrier material. Carrier materials which may
be used are the actual polyester used or else other polymers
sufficiently compatible therewith.
[0047] An important factor in masterbatch technology is that the
particle size and the bulk density of the masterbatch are similar
to the particle size and bulk density of the polyester, enabling
homogeneous dispersion and thus homogeneous UV stabilization.
[0048] The base layer B and any intermediate layers present may
also comprise customary additives, such as stabilizers and/or
antiblocking agents. The two other outer layers preferably also
comprise customary additives, such as stabilizers and/or
antiblocking agents. It is appropriate for these to be added to the
polymer or, respectively, polymer mixture straight away prior to
melting. Examples of stabilizers used are phosphorous compounds,
such as phosphoric acid or phosphoric esters.
[0049] Suitable antiblocking agents (in this context also termed
pigments) are inorganic and/or organic particles, such as calcium
carbonate, amorphous silica, talc, magnesium carbonate, barium
carbonate, calcium sulfate, barium sulfate, lithium phosphate,
calcium phosphate, magnesium phosphate, aluminum oxide, LiF, the
calcium, barium, zinc or manganese salts of the dicarboxylic acids
used, carbon black, titanium dioxide, kaolin or crosslinked
polystyrene particles or crosslinked acrylate particles.
[0050] The antiblocking agents selected may also be mixtures of two
or more different antiblocking agents or mixtures of antiblocking
agents of the same composition but different particle size. The
particles may be added to the individual layers at the respective
advantageous concentrations, e.g. as a glycolic dispersion during
the polycondensation or by way of masterbatches during
extrusion.
[0051] Preferred particles are SiO2 in colloidal or in chain form.
These particles become very well bound into the polymer matrix and
create only very few vacuoles. Vacuoles generally cause haze and it
is therefore appropriate to avoid these. There is no restriction in
principle on the diameters of the particles used. However, it has
proven appropriate for achieving the object to use particles with
an average primary particle diameter below 100 nm, preferably below
60 nm and particularly preferably below 50 nm, and/or particles
with an average primary particle diameter above 1 .mu.m, preferably
above 1.5 .mu.m and particularly preferably above 2 .mu.m. However,
the average particle diameter of these particles described last
should not be above 5 .mu.m.
[0052] To achieve the abovementioned properties of the sealable
film, it has also proven to be appropriate to select a particle
concentration in the base layer B which is lower than in the two
outer layers A and C. In a three-layer film of the type mentioned
the particle concentration in the base layer B will be from 0 to
0.15% by weight, preferably from 0 to 0.12% by weight and in
particular from 0 to 0.10% by weight. There is no restriction in
principle on the diameter of the particles used, but particular
preference is given to particles with an average diameter above 1
.mu.m.
[0053] In its advantageous usage form, the film is composed of
three layers: the base layer B and, applied on both sides of this
base layer, outer layers A and C, and outer layer A is sealable
with respect to itself and with respect to outer layer C.
[0054] To achieve the property profile mentioned for the film, the
outer layer C preferably has more pigment (i.e. a higher pigment
concentration) than the outer layer A. The pigment concentration in
this outer layer C is from 0.1 to 1.0% by weight, advantageously
from 0.12 to 0.8% by weight and in particular from 0.15 to 0.6% by
weight. In contrast, the other outer layer A, which is sealable and
positioned opposite to the outer layer C, has a lower degree of
filling with inert pigments. The concentration of the inert
particles in layer A is from 0.01 to 0.2% by weight, preferably
from 0.015 to 0.15% by weight and in particular from 0.02 to 0.1%
by weight.
[0055] Between the base layer and the outer layers there may, if
desired, also be intermediate layers, preferably one intermediate
layer. This may again be composed of the polymers described for the
base layers. In one particularly preferred embodiment, it is
composed of the polyester used for the base layer. It may also
comprise the additives described. The thickness of an intermediate
layer is generally above 0.3 .mu.m, preferably in the range from
0.5 to 15 .mu.m, in particular in the range from 1.0 to 10 .mu.m
and very particularly preferably in the range from 1.0 to 5
.mu.m.
[0056] In the particularly advantageous three-layer embodiment of
the novel film, the thickness of the outer layers A and C is
generally above 0.1 .mu.m, and is generally in the range from 0.2
to 4.0 .mu.m, advantageously in the range from 0.2 to 3.5 .mu.m, in
particular in the range from 0.3 to 3 .mu.m and very particularly
preferably in the range from 0.3 to 2.5 .mu.m, and the thicknesses
of the outer layers A and C may be identical or different.
[0057] The total thickness of the novel polyester film may vary
within wide limits. It is preferably from 3 to 80 .mu.m, in
particular from 4 to 50 .mu.m, particularly preferably from 5 to 30
.mu.m, the layer B preferably making up from 5 to 90% of the total
thickness.
[0058] In producing the film, it is appropriate for the polymers
for the base layer B and the two outer layers A and C to be
introduced separately to three extruders. Any foreign bodies or
contamination present may be filtered out from the polymer melt
prior to extrusion.
[0059] The melts are then extruded through a coextrusion die to
give flat melt films, and layered one upon the other. The
multilayer film is then drawn off and solidified with the aid of a
chill roll and, if desired, other rolls.
[0060] The invention therefore also provides a process for
producing the novel polyester film by the coextrusion process known
per se.
[0061] The procedure for this process is that the melts
corresponding to the individual layers of the film are coextruded
through a flat-film die, the resultant film is drawn off for
solidification on one or more rolls, the film is then biaxially
stretched (oriented), and the biaxially stretched film is heat-set
and, if desired, corona- or flame-treated on the surface layer
intended for treatment.
[0062] The biaxial stretching (orientation) is generally carried
out sequentially, and preference is given to sequential biaxial
stretching in which stretching is first longitudinal (in the
machine direction) and then transverse (perpendicular to the
machine direction).
[0063] As is usual in coextrusion, the polymer or the polymer
mixture for the individual layers is first compressed and
plasticized in an extruder, and the additives used may already be
present in the polymer or the polymer mixture during this process.
The melts are then simultaneously extruded through a flat-film die
(slot die), and the extruded multilayer film is drawn off on one or
more take-off rolls, whereupon it cools and solidifies.
[0064] The biaxial orientation is generally carried out
sequentially, preferably orienting first longitudinally (i.e. in
the machine direction=MD) and then transversely (i.e.
perpendicularly to the machine direction=TD). This gives
orientation of the molecular chains. The longitudinal orientation
can be carried out with the aid of two rolls running at different
speeds corresponding to the desired stretching ratio. For the
transverse orientation use is generally made of an appropriate
tenter frame.
[0065] The temperature at which the orientation is carried out may
vary over a relatively wide range and depends on the film
properties desired. The longitudinal stretching is generally
carried out at from about 80 to 130.degree. C., and the transverse
stretching at from about 80 to 150.degree. C. The longitudinal
stretching ratio is generally in the range from 2.5:1 to 6:1,
preferably from 3:1 to 5.5:1. The transverse stretching ratio is
generally in the range from 3.0:1 to 5.0:1, preferably from 3.5:1
to 4.5:1. Prior to the transverse stretching, one or both surfaces
of the film may be in-line coated by known processes. The in-line
coating may serve, for example, to give improved adhesion of a
metal layer or of any printing ink applied, or else to improve
antistatic performance or processing performance.
[0066] For producing a film with very good sealing properties it
has proven advantageous for the planar orientation .DELTA.p of the
film to be equal to or less than 0.165, but particularly less than
0.163. In this case the strength of the film in the direction of
its thickness is so great that when the seal seam strength is
measured it is specifically the seal seam which separates, and the
tear does not enter the film or propagate therein.
[0067] The significant variables affecting the planar orientation
.DELTA.p have been found to be the longitudinal and transverse
stretching parameters, and also the SV (standard viscosity) of the
raw material used. The processing parameters include in particular
the longitudinal and transverse stretching ratios (.lambda.MD and
.lambda.TD), the longitudinal and transverse stretching
temperatures (TMD and TTD), the film web speed and the nature of
the stretching, in particular that in the longitudinal direction of
the machine. For example, if the planar orientation .DELTA.p
obtained with a machine is 0.167 with the following set of
parameters: .lambda.MD=4.8 and .lambda.TD=4.0, a longitudinal
stretching temperature TMD of from 80-118.degree. C. and a
transverse stretching temperature TTD of from 80-125.degree. C.,
then increasing the longitudinal stretching temperature TMD to
80-125.degree. C. or increasing the transverse stretching
temperature TTD to 80-135.degree. C., or lowering the longitudinal
stretching ratio .lambda.MD to 4.3 or lowering the transverse
stretching ratio .lambda.TD to 3.7 gives a planar orientation
.DELTA.p within the desired range. The film web speed here is 340
m/min and the SV (standard viscosity) of the material is about 730.
For the longitudinal stretching, the data mentioned are based on
what is known as N-TEP stretching, composed of a low-orientation
stretching step (LOE, Low Orientation Elongation) and a
high-orientation stretching step (REP, Rapid Elongation Process).
Other stretching systems in principle give the same ratios, but the
numeric values for each process parameter may be slightly
different. The temperatures given are based on the respective roil
temperatures in the case of the longitudinal stretching and on
infrared-measured film temperatures in the case of the transverse
stretching.
[0068] In the heat-setting which follows, the film is held for from
0.1 to 10 s at a temperature of from about 150 to 250.degree. C.
The film is then wound up in a usual manner.
[0069] After the biaxial stretching it is preferable for one or
both surfaces of the film to be corona- or flame-treated by one of
the known methods. The intensity of the treatment generally gives a
surface tension in the range above 45 mN/m.
[0070] The film may also be coated in order to achieve other
desired properties. Typical coatings are layers with
adhesion-promoting, antistatic, slip-improving or release action.
These additional layers may, of course, be applied to the film by
way of in-line coating, using aqueous dispersions, prior to the
transverse stretching step.
[0071] The novel film has excellent sealability, very good UV
resistance, very good handling properties and very good processing
performance. The sealable outer layer A of the film seals not only
with respect to itself (fin sealing) but also with respect to the
nonsealable outer layer C (lap sealing). The minimum sealing
temperature for the lap sealing here is only about 10.degree. C.
higher than the fin-sealing temperature, and the particular that in
the longitudinal direction of the machine. For example, if the
planar orientation .DELTA.p obtained with a machine is 0.167 with
the following set of parameters: .lambda.MD=4.8 and .lambda.TD=4.0,
a longitudinal stretching temperature TMD of from 80-118.degree. C.
and a transverse stretching temperature TTD of from 80-125.degree.
C., then increasing the longitudinal stretching temperature TMD to
80-125.degree. C. or increasing the transverse stretching
temperature TTD to 80-135.degree. C., or lowering the longitudinal
stretching ratio .lambda.MD to 4.3 or lowering the transverse
stretching ratio .lambda.TD to 3.7 gives a planar orientation
.DELTA.p within the desired range. The film web speed here is 340
m/min and the SV (standard viscosity) of the material is about 730.
For the longitudinal stretching, the data mentioned are based on
what is known as N-TEP stretching, composed of a low-orientation
stretching step) (LOE, Low Orientation Elongation) and a
high-orientation stretching step (REP, Rapid Elongation Process).
Other stretching systems in principle give the same ratios, but the
numeric values for each process parameter may be slightly
different. The temperatures given are based on the respective roll
temperatures in the case of the longitudinal stretching and on
infrared-measured film temperatures in the case of the transverse
stretching.
[0072] In the heat-setting which follows, the film is held for from
0.1 to 10 s at a temperature of from about 150 to 250.degree. C.
The film is then wound up in a usual manner.
[0073] After the biaxial stretching it is preferable for one or
both surfaces of the film to be corona- or flame-treated by one of
the known methods. The intensity of the treatment generally gives a
surface tension in the range above 45 mN/m.
[0074] The film may also be coated in order to achieve other
desired properties. Typical coatings are layers with
adhesion-promoting, antistatic, slip-improving or release action.
These additional layers may, of course, be applied to the film by
way of in-line coating, using aqueous dispersions, prior to the
transverse stretching step.
[0075] The novel film has excellent sealability, very good UV
resistance, very good handling properties and very good processing
performance. The sealable outer layer A of the film seals not only
with respect to itself (fin sealing) but also with respect to the
nonsealable outer layer C (lap sealing). The minimum sealing
temperature for the lap sealing here is only about 10.degree. C.
higher than the fin-sealing temperature, and the reduction in the
seal seam strength is not more than 0.3 N/15 mm.
[0076] The gloss and haze of the film are also improved over films
of the prior art. In producing the novel film it is certain that
material for recycling can be refed to the extrusion process at a
concentration of from 20 to 60% by weight, based on the total
weight of the film, without any significant adverse effect on the
physical properties of the film.
[0077] The excellent sealing properties, very good handling
properties and very good processing properties of the film make it
particularly suitable for processing on high-speed machinery.
[0078] A film of this type is therefore also cost-effective.
[0079] The excellent combination of properties possessed by the
film, furthermore, makes it suitable for a wide variety of
different applications, for example for interior decoration, for
constructing exhibition stands, for exhibition requisites, for
displays, for placards, for protective glazing of machines or of
vehicles, in the lighting sector, in the fitting out of shops or of
stores, or as a promotional requisite or laminating medium.
[0080] The good UV resistance of the novel, transparent film
moreover makes it suitable for outdoor applications, e.g. for
greenhouses, roofing systems, exterior cladding, protective
coverings for materials, e.g. for steel sheet, applications in the
building sector and illuminated advertising profiles.
[0081] The table below (Table 1) gives once again the most
important film properties according to the invention.
1TABLE 1 Range according Particularly to the invention Preferred
preferred Unit Test method Outer layer A Minimum sealing
temperature <110 <105 <100 .degree. C. internal Seal seam
strength >1.3 >1.5 >1.8 N/15 mm internal Average roughness
Ra <30 <25 <20 nm DIN 4768, cut-off 0.25 mm Range of
values for gas flow 500-4000 800-3500 1000-3000 sec internal
measurement Gloss, 20.degree. >120 >130 >140 DIN 67 530
Outer layer C COF <0.5 <0.45 <0.40 DIN 53 375 Average
roughness Ra 40-100 45-95 50-90 nm DIN 4768, cut-off 0.25 mm Range
of values for gas flow <120 <100 <80 sec internal
measurement Gloss, 20.degree. >140 >150 >160 DIN 67 530
Other film properties Haze <4 <3 <2.5 % ASTM-D 1003-52
Planar orientation <0.165 <0.163 <0.160 internal
Weathering test, UV resistance <20% ISO 4892 Change in
propertiesi) i)The films were weathered both sides, in each case
for 1000 hours per side, using the Atlas Ci 65 Weather-Ometer to
the test specification ISO 4892, and then
[0082] The following test methods were used to measure the
properties of the raw materials and of the films:
[0083] DIN=Deutsches Institut fur Normung
[0084] ISO=International Organization for Standardization
[0085] ASTM=American Society for Testing and Materials
[0086] SV (DCA), IV (DCA)
[0087] The standard viscosity SV (DCA) is measured in
dichloroacetic acid by a method based on DIN 53726.
[0088] The intrinsic viscosity (IV) is calculated as follows from
the standard viscosity
IV (DCA)=6.67.multidot.10-4SV.multidot.(DCA)+0.118
[0089] Determination of Minimum Sealing Temperature
[0090] Hot-sealed specimens (seal seam 20 mm.times.100 mm) are
produced with a Brugger HSG/ET sealing apparatus, by sealing the
film at different temperatures with the aid of two heated sealing
jaws at a sealing pressure of 2 bar and with a sealing time of 0.5
s. From the sealed specimens test strips of 15 mm width were cut.
The T-seal seam strength was measured as in the determination of
seal seam strength. The minimum sealing temperature is the
temperature at which a seal seam strength of at least 0.5 N/15 mm
is achieved.
[0091] Seal Seam Strength
[0092] To determine the seal seam strength, two film strips of
width 15 mm were placed one on top of the other and sealed at
130.degree. C. with a sealing time of 0.5 s and a sealing pressure
of 2 bar (apparatus: Brugger model NDS, single-side-heated sealing
jaw). The seal seam strength was determined by the T-peel
method.
[0093] Coefficient of Friction
[0094] The coefficient of friction was determined to DIN 53 375.
The coefficient of sliding friction was measured 14 days after
production.
[0095] Surface Tension
[0096] Surface tension was determined by what is known as the ink
method (DIN 53 364).
[0097] Haze
[0098] The Holz haze was measured by a method based on ASTM-D
1003-52 but, in order to utilize the most effective measurement
range, measurements were made on four pieces of film laid one on
top of the other, and a 1.degree. slit diaphragm was used instead
of a 4.degree. pinhole.
[0099] Gloss
[0100] Gloss was determined to DIN 67 530. The reflectance was
measured as an optical value characteristic of a film surface.
Based on the standards ASTM-D 523-78 and ISO 2813, the angle of
incidence was set at 20.degree.. A beam of light hits the flat test
surface at the set angle of incidence and is reflected and/or
scattered thereby. A proportional electrical variable is displayed
representing light rays hitting the photoelectronic detector. The
value measured is dimensionless and must be stated together with
the angle of incidence.
[0101] Determination of Particle Sizes on Film Surfaces
[0102] A scanning electron microscope and an image analysis system
were used to determine the size distribution of elevations on film
surfaces. Use is made of the XL30 CP scanning electron microscope
from Philips with an integrated image analysis program: AnalySIS
from Soft-imaging System.
[0103] For these measurements, specimens of film are placed flat on
a specimen holder. These are then metalized obliquely at an angle
"a" with a thin metallic layer (e.g. of silver). The symbol "a"
here is the angle between the surface of the specimen and the
direction of diffusion of the metal vapor. This oblique
metalization throws a shadow behind the elevation. Since the
shadows are not at this stage electrically conductive, the specimen
is then further spotted or metalized with a second metal (e.g.
gold), the second coating here impacting vertically onto the
surface of the specimen in such a way as not to produce any shadows
in the second coating.
[0104] Scanning electron microscope (SEM) images are taken of the
specimen surfaces prepared in this way. The shadows of the
elevations are visible because of the contrast of the metallic
materials. The specimen is oriented in the SEM in such as way that
the shadows run parallel to one edge of the image. The following
conditions are set in the SEM for recording the image: secondary
electron detector, operating distance 10 mm, acceleration voltage
10 kV and spot 4.5. The brightness and contrast are set in such a
way that all of the information in the image is represented as gray
values and the intensity of the background noise is sufficiently
small for it not to be detected as a shadow. The length of the
shadows is measured by image analysis. The threshold value for
shadow identification is set at the point where the second
derivative of the gray value distribution of the image passes
through the zero point. Before shadow identification, the image is
smoothed with an NxN filter (size 3, 1 iteration). A frame is set
so as to ensure that elevations which are not reproduced in their
entirety in the image are not included in the measurements. The
magnification, the size of the frame and the number of images
evaluated are selected in such a way that a total film surface of
0.36 mm2 is evaluated.
[0105] The height of the individual elevations is computed from the
individual shadow lengths using the following relationship:
h=(tan a)*L
[0106] where h is the height of the elevation, a is the
metalization angle and L is the shadow length. The elevations
recorded in this way are classified so as to arrive at a frequency
distribution. The classification is into classes of 0.05 .mu.m
width between 0 and 1 .mu.m, the smallest class (from 0 to 0.05
.mu.m) not being used for further evaluation calculations. The
diameters (dimension perpendicular to the direction of shadow
throw) of the elevations are classified in a similar way in classes
of 0.2 .mu.m width from 0 to 10 .mu.m, and here again the smallest
class is not used for further evaluation.
[0107] Surface Gas Flow Time
[0108] The principle of the test method is based on the air flow
between one side of the film and a smooth silicon wafer sheet. The
air flows from the surroundings into an evacuated space, and the
interface between film and silicon wafer sheet acts as a flow
resistance. A round specimen of film is placed on a silicon wafer
sheet in the middle of which there is a hole providing the
connection to the receiver. The receiver is evacuated to a pressure
below 0.1 mbar. The time in seconds taken by the air to establish a
pressure rise of 56 mbar in the receiver is determined.
2 Test conditions: Test area 45.1 cm.sup.2 Weight applied 1276 g
Air temperature 23.degree. C. Humidity 50% relative humidity
Aggregated gas volume 1.2 cm.sup.3 Pressure difference 56 mbar
[0109] Determination of Planar Orientation .DELTA.p
[0110] Planar orientation is determined by measuring the refractive
index with an Abbe refractometer.
[0111] Preparation of Specimens
[0112] Specimen size and length: from 60 to 100 mm
[0113] Specimen width: corresponds to prism width of 10 mm
[0114] To determine nMD and na (=nz), the specimen to be tested has
to be cut out from the film with the running edge of the specimen
running precisely in the direction TD. To determine nMD and na
(=nz), the specimen to be tested has to be cut out from the film
with the running edge of the specimen running precisely in the
direction MD. The specimens are to be taken from the middle of the
film web. Care must be taken that the temperature of the Abbe
refractometer is 23.degree. C. Using a glass rod, a little
diiodomethane (N=1.745) or diiodomethane-bromonaphthalene mixture
is applied to the lower prism, which has been cleaned thoroughly
before the test. The refractive index of the mixture must be
greater than 1.685. The specimen cut out in the direction TD is
firstly laid on top of this, in such a way that the entire surface
of the prism is covered. Using a paper wipe, the film is now firmly
pressed flat onto the prism, so that it is firmly and smoothly
positioned thereon. The excess liquid must be sucked away. A little
of the test liquid is then dropped onto the film. The second prism
is swung down and into place and pressed firmly into contact. The
right-hand knurled screw is then used to turn the indicator scale
until a transition from light to dark can be seen in the field of
view in the range from 1.62 to 1.68. If the transition from light
to dark is not sharp, the colors are brought together using the
upper knurled screw in such a way that only one light and one dark
zone are visible. The sharp transition line is brought to the
crossing point of the two diagonal lines (in the eyepiece) using
the lower knurled screw. The value now indicated on the measurement
scale is read off and entered into the test record. This is the
refractive index nMD in the machine direction. The scale is now
turned using the lower knurled screw until the range visible in the
eyepiece is from 1.49 to 1.50.
[0115] The refractive index na or nz (in the direction of the
thickness of the film) is then determined. To improve the
visibility of the transition, which is only weakly visible, a
polarization film is placed over the eyepiece. This is turned until
the transition is clearly visible. The same considerations apply as
in the determination of nMD. If the transition from light to dark
is not sharp (colored), the colors are brought together using the
upper knurled screw in such a way that a sharp transition can be
seen. This sharp transition line is placed on the crossing point of
the two diagonal lines using the lower knurled screw, and the value
indicated on the scale is read off and entered into the table. The
specimen is then turned, and the corresponding refractive indices
nMD and na (=nz) of the other side are measured and entered into an
appropriate table.
[0116] After determining the refractive indices in, respectively,
the direction MD and the direction of the thickness of the film,
the specimen strip cut out in the direction MD is placed in
position and the refractive indices nTD and na (=nz) are determined
accordingly. The strip is turned over, and the values for the B
side are measured. The values for the A side and the B side are
combined to give average refractive indices. The orientation values
are then calculated from the refractive indices using the following
formulae:
.DELTA.n=nMD-nTD
.DELTA.p=(nMD+nTD)/2-nz
nav=(nMD+nTD+nz)/3
[0117] Surface Defects
[0118] Surface defects are determined visually.
[0119] Mechanical Properties
[0120] Modulus of elasticity, tear strength and elongation at break
are measured longitudinally and transversely to ISO 527-1-2.
[0121] Weathering (on Both Sides), UV Resistance
[0122] UV resistance is tested as follows to the test specification
ISO 4892
3 Test apparatus: Atlas Ci 65 Weather-Ometer Test conditions: ISO
4892, i.e. artificial weathering Irradiation time: 1000 hours (per
side) Irradiation: 0.5 W/m2, 340 nm Temperature: 63.degree. C.
Relative humidity: 50% Xenon lamp: inner and outer filter made from
borosilicate Irradiation cycles: 102 minutes of UV light, then 18
minutes of UV light with water spray on the specimens, then again
102 minutes of UV light, etc. Color change The change in color of
the specimens after artificial weathering is measured using a
spectrophotometer to DIN 5033.
[0123] The greater the numerical deviation from standard, the
greater the color difference. Numerical values of <0.3 can be
neglected and indicate that there is no significant color
change.
[0124] Yellowness
[0125] The Yellowness Index YID is the deviation from the colorless
condition in the "yellow" direction, and is measured to DIN 6167.
Yellowness values (YID)<5 are not visually detectable.
EXAMPLE 1
[0126] Chips made from polyethylene terephthalate (prepared by the
transesterification process with Mn as transesterification
catalyst, Mn concentration: 100 ppm) were dried at 150.degree. C.
to residual moisture below 100 ppm and, together with the stated
masterbatches, fed to the extruder for the base layer B. Chips made
from polyethylene terephthalate were likewise fed, together with
the masterbatches stated, to the extruder for the nonsealable outer
layer C.
[0127] Alongside this, chips were prepared made from a linear
polyester which is composed of an amorphous copolyester with 78 mol
% of ethylene terephthalate and 22 mol % of ethylene isophthalate
(prepared via the transesterification process with Mn as
transesterification catalyst, Mn concentration: 100 ppm) The
copolyester was dried at a temperature of 100.degree. C. to a
residual moisture below 200 ppm and, together with the
masterbatches stated, fed to the extruder for the sealable outer
layer A.
[0128] The UV stabilizer
2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphe- nol
(.RTM.Tinuvin 1577) is fed in the form of masterbatches. The
masterbatches are composed of 5% by weight of Tinuvin 1577 as
active component and 95% by weight of polyethylene terephthalate
(for outer layer C) and, respectively, 95% by weight of
polyethylene isophthalate (for outer layer A). The masterbatches
with 5% by weight of Tinuvin 1577 are fed only to the two thick
outer layers at 20% by weight via masterbatch technology.
[0129] The masterbatch is charged at room temperature from a
separate metering vessel into a vacuum dryer, which from the time
of charging to the end of the residence time passes through a
temperature profile of from 25 to 130.degree. C. During the
residence time of about hours, the masterbatch is stirred at 61
rpm. The precrystallized or predried masterbatch is after-dried in
the downstream hopper, likewise in vacuo, at 140.degree. C. for 4
hours.
[0130] Coextrusion, followed by stepwise longitudinal and
transverse orientation, is used to produce a transparent
three-layer film with ABC structure and with a total thickness of
12 .mu.m. The thickness of each outer layer can be found in Table
2.
4 Outer layer A is a mixture made from: 20.0% by weight of UV
masterbatch based on polyethylene isophthalate 77.0% by weight of
copolyester with an SV of 800 3.0% by weight of masterbatch made
from 97.75% by weight of copolyester (SV of 800) and 1.0% by weight
of Sylobloc .RTM. 44 H (synthetic SiO2 from Grace) and 1.25% by
weight of Aerosil .RTM. TT 600 (chain-type SiO2 from Degussa) Base
layer B: 100% by weight of polyethylene terephthalate with an SV of
800 Outer layer C is a mixture made from: 20.0% by weight of UV
masterbatch based on polyethylene tere- phthalate 68% by weight of
polyethylene terephthalate with an SV of 800 12% by weight of
masterbatch made from 97.75% by weight of copolyester (SV of 800)
and 1.0% by weight of Sylobloc .RTM. 44 H (synthetic SiO2 from
Grace) and 1.25% by weight of Aerosil .RTM. TT 600 (chain-type SiO2
from Degussa)
[0131] The production conditions in the individual steps of the
process were:
5 Extrusion: Temperatures A layer: 270.degree. C. B layer:
290.degree. C. C layer: 290.degree. C. Die gap width: 2.5 mm
Take-off roll 30.degree. C. Temperature: Longitudinal Temperature:
80-125.degree. C. stretching: Longitudinal 4.2 stretching ratio:
Transverse Temperature: 80-135.degree. C. stretching: Transverse
4.0 stretching ratio: Heat-setting: Temperature: 230.degree. C.
Duration: 3 s
[0132] The film had the required good sealing properties and
exhibits the desired handling properties and the desired processing
performance. The film structure and the properties achieved in
films prepared in this way are given in Tables 2 and 3
(CE=Comparative Example).
[0133] The films in this example, and in all of the examples below,
were weathered on both sides, in each case for 1000 hours per side,
using the Atlas Ci 65 Weather-Ometer to test specification ISO 4892
and then tested for mechanical properties, discoloration, surface
defects, haze and gloss (cf. Table 4).
EXAMPLE 2
[0134] In comparison with Example 1, the outer layer thickness of
the sealable layer A was raised from 1.5 to 2.0 .mu.m. This has
given improved sealing properties, and in particular the seal seam
strength has increased markedly.
EXAMPLE 3
[0135] In comparison with Example 1, the film produced now had a
thickness of 20 .mu.m. The outer layer thickness for the sealable
layer A was 2.5 .mu.m and that for the nonsealable layer C was 2.0
.mu.m. This has again improved sealing properties, and in
particular the seal seam strength has increased markedly, and the
handling properties of the film have improved slightly.
EXAMPLE 4
[0136] In comparison with Example 3, the copolymer for the sealable
outer layer A has been changed. Instead of the amorphous
copolyester with 78 mol % of ethylene terephthalate and 22 mol % of
ethylene isophthalate, use was now made of an amorphous copolyester
with 70 mol % of ethylene terephthalate and 30 mol % of ethylene
isophthalate. The polymer was processed in a twin-screw vented
extruder, without any need for predrying. The outer layer thickness
for the sealable layer A was again 2.5 .mu.m, and that for the
nonsealable layer C was 2.0 .mu.m. This has given improved sealing
properties, and in particular the seal seam strength has increased
markedly. To achieve good handling properties and good processing
performance from the film, the pigment concentration in the two
outer layers was raised slightly.
COMPARATIVE EXAMPLE 1
[0137] In comparison with Example 1, the sealable outer layer A was
now not pigmented. Although this has given some improvement in the
sealing properties, the handling properties of the film and its
processing performance have worsened markedly.
COMPARATIVE E 2
[0138] In comparison with Example 1, the level of pigmentation in
the sealable outer layer A was now as high as in the nonsealable
outer layer C. This measure has improved the handling properties
and the processing properties of the film, but the sealing
properties have worsened markedly.
Comparative Example 3
[0139] In comparison with Example 1, the nonsealable outer layer C
was now pigmented to a markedly lower level. The handling
properties of the film and its processing performance have worsened
markedly.
Comparative Example 4
[0140] Example I from EP-A 0 035 835 was repeated. The sealing
performance of the film, its handling properties and its processing
performance are markedly poorer than in the examples according to
the invention.
6 TABLE 2 Pigment Film Layer thicknesses Average pigment
concentrations thickness Film .mu.m Pigments in layers diameter in
layers mm ppm (parts by weight) Example .mu.m structure A B C A B C
A B C A B C E 1 12 ABC 1.5 9 1.5 Sylobloc 44 H none Sylobloc 44 H
2.5 2.5 300 0 1200 Aerosil TT 600 Aerosil TT 600 0.04 0.04 375 1500
E 2 12 ABC 2.0 8.5 1.5 Sylobloc 44 H none Sylobloc 44 H 2.5 2.5 300
0 1200 Aerosil TT 600 Aerosil TT 600 0.04 0.04 375 1500 E 3 20 ABC
2.5 15.5 2.0 Sylobloc 44 H none Sylobloc 44 H 2.5 2.5 300 0 1200
Aerosil TT 600 Aerosil TT 600 0.04 0.04 375 1500 E 4 20 ABC 2.5
15.5 2.0 Sylobloc 44 H none Sylobloc 44 H 2.5 2.5 400 0 1500
Aerosil TT 600 Aerosil TT 600 0.04 0.04 500 1875 CE 1 12 ABC 1.5 9
1.5 none none Sylobloc 44 H 2.5 0 1200 Aerosil TT 600 0.04 1500 CE
2 12 ABC 1.5 9 1.5 Sylobloc 44 H none Sylobloc 44 H 2.5 2.5 300 0
1200 Aerosil TT 600 Aerosil TT 600 0.04 0.04 375 1500 CE 3 12 ABC
1.5 9 1.5 Sylobloc 44 H none Sylobloc 44 H 2.5 2.5 300 0 600
Aerosil TT 600 Aerosil TT 600 0.04 0.04 375 750 CE 4 15 AB 2.25
12.75 Gasil 35 none 3 2500 0 EP-A 035 835
[0141]
7 TABLE 3 Minimum Coeffic- sealing Seal seam ient of temperature
strength COF Average Values Winding .degree. C. N/15 mm C side
roughness measured for Constants Gloss perform- Process- A side
with A side with with Ra nm gas flow sec A/B 20.degree. ance and
ing respect to respect to respect to A C A C A C A C handling
perfor- Example A side A side C side side side side side side side
Dp side side Haze properties mance E 1 100 2.0 0.45 25 65 1200 80
0.5 3.06 0.165 140 170 2.5 ++ ++ E 2 98 2.7 0.45 26 65 1280 80 0.5
3.06 0.165 140 170 2.5 ++ ++ E 3 95 3.0 0.41 23 61 1110 80 0.5 3.06
0.165 130 170 3.0 ++ ++ E 4 85 3.3 0.40 23 65 1300 60 0.5 3.06
0.165 130 170 3.0 ++ ++ CE 1 98 2.1 0.45 10 65 10,000 80 0.165 160
170 1.5 - - CE 2 110 1.0 0.45 65 65 80 80 0.165 130 170 2.8 - - CE
3 100 2.0 0.45 25 37 1200 150 0.165 160 190 1.5 - - CE 4 115 0.97
>2 70 20 50 >5000 12 - - Key to winding performance, handling
properties and processing performance of films: ++: no tendency to
adhere to rolls or to other mechanical parts, no blocking problems
on winding or during processing on packaging machinery, low
production costs -: tendency to adhere to rolls or other mechanical
parts, blocking problems on winding and during processing on
packaging machinery, high production costs due to complicated
handling of film in machinery
[0142]
8 TABLE 4 Modulus of elasticity Tear strength Elongation at break
Total Gloss N/mm2 N/mm2 % discoloration Surface A C Example
Weathering longitudinal transverse longitudinal transverse
longitudinal transverse value defects side side Haze E 1 Before
4300 5800 220 280 170 100 0.2 none 140 170 2.5 After 4100 5480 190
270 150 90 132 165 2.8 E 2 Before 4200 5600 215 260 170 100 2.5
none 140 170 2.5 After 4030 5400 190 250 150 90 138 165 2.8 E 3
Before 4500 5700 230 280 175 105 0.24 none 130 170 3.0 After 4000
5350 196 255 150 89 138 155 3.7 E 4 Before 4300 5800 220 275 178
111 0.27 none 130 170 3.0 After 3900 5360 192 248 148 92 138 165
3.5
* * * * *